1. Field of the Invention
The present invention relates to a gas processing technology, in particular, to a gas processing apparatus, a baffle member, and a gas processing method for use in fabrication of semiconductor devices.
2. Description of the Related Art
When semiconductor devices are fabricated, a gas processing apparatus that supplies various types of gas to a processing chamber and performs a predetermined process for a workpiece is used.
As an example of such a gas processing apparatus, a CVD (Chemical Vapor Deposition) apparatus is known.
In the CVD apparatus, various types of gas as row materials are supplied to a workpiece such as a wafer disposed in a processing chamber. Using thermal energy of the wafer, plasma excitation, and so forth, gas as a chemically active reaction seed causes a thin film to be formed on the wafer. Thus, to equally form a thin film on the entier surface of the wafer using such an apparatus, it is necessary to uniformly supply the gas to the entire surface of the wafer.
To uniformly supply a gas to the entire surface of the wafer, in the CVD apparatus, a gas processing apparatus that has a gas supplying means and a shower head is used. The gas supplying means is disposed at a position where it faces the processing surface of the wafer. The shower head is structured as shown in FIG. 13. The shower head supplies the gas to the wafer.
FIG. 13 is a sectional view showing the structure in the vicinity of the shower head of the gas processing apparatus.
As shown in FIG. 13, the shower head 41 is disposed so that the bottom surface as the spray side of the shower head 41 faces a wafer 42. A gas delivery pipe 43 is connected to an upper portion of the shower head 41. The gas delivery pipe 43 causes the gas to be delivered to the interior of the shower head 41. A spray plate 44 is disposed at a lower portion of the shower head 41. The spray plate 44 composes a bottom side partition wall of the shower head 41. Many spray holes 45 are formed as gas spray holes on the spray plate 44. The gas delivered from the gas delivery pipe 43 to the interior of the shower head 41 is supplied to the surface of the wafer 42 through the spray holes 45.
A shower head that has a plate with many small through-holes that cause the difference between the gas flow amount of the gas that sprays from the center of the shower head and the gas flow amount of the gas that sprays from the periphery thereof to decrease has been proposed. The plate is termed baffle plate. An example of the structure of the baffle plate is shown in FIG. 14.
FIG. 14 is a sectional view showing the structure in the vicinity of a shower head of a gas processing apparatus having a baffle plate.
As shown in FIG. 14, a baffle plate 47 having many through-holes is disposed between a spray plate 44 of a shower head 41 and a connecting portion of a gas delivery pipe 43. With the baffle plate 47, gas delivered from the gas delivery pipe 43 is temporarily stored in a baffle space 48 on the upstream side of the baffle plate 47.
Thus, the irregularity of dynamic pressure of the gas delivered from the gas delivery pipe 43 decreases. Consequently, the flow amount of the gas that flows in the through-holes 46 becomes almost equal. The resultant gas is supplied to a shower pre-chamber 49 on the downstream side of the baffle plate 47.
Thus, the irregularity of the pressure in the shower pre-chamber 49 decreases. Consequently, the flow amount of the gas sprayed from the spray plate becomes constant. Thus, the gas is uniformly supplied to the entire surface of the wafer 42.
To cause the flow amount of the gas that flows in the through-holes 46 to be equal, it is effective to decrease the hole diameters of the through-holes 46 so as to increase the flow pressure loss of the through-holes 46. When the hold diameters of the through-holes 46 are decreased, the pressure in the baffle space 48 rises and thereby the irregularity of the pressure due to the dynamic pressure of the gas decreases. In addition, since the difference between the pressure of the upper portion and the pressure of the lower portion (the pressure in the baffle space 48 and the pressure in the shower pre-chamber 49) of the baffle plate 47 becomes large. Thus, the pressure at each position of the baffle plate 47 becomes almost equal. As a result, the flow amount of the gas that flows in the through-holes 46 becomes almost equal.
However, due to the restriction of the machining accuracy, the cost restriction, the limitation of the pressure on the upstream side of the baffle plate 47, and so forth, the hole diameters of the through-holes 46 cannot be satisfactorily decreased. Thus, the gas cannot be uniformly supplied to the entire surface of the wafer 42.
In addition, as the hole diameters of the through-holes 46 decrease, the flow rate of the gas increases. Thus, the dynamic pressure of the gas that flow from the through-holes 46 increases. Thus, the backing pressure of the spray holes 45 in the vicinity of the lower portion of the through-holes 46 locally rises. Consequently, the flow amounts of the spray holes 45 become irregular.
In a related art reference disclosed as Japanese Patent Laid-Open Publication No. 1-139771, spray holes are formed in such a manner that the hole diameters on the gas outlet side are larger than those on the gas inlet side. Thus, since gas that flows in the spray holes expands and diffuses on the outlet side, the gas uniformly sprays.
However, according to such a related art reference, gas is uniformly sprayed from each spray hole. In other words, the flow amount of gas sprayed from spray holes at the center portion of the spray plate is different from that at the peripheral portion of the spray plate. Thus, according to the related art reference, gas cannot be uniformly supplied to the entire surface of the wafer.
The present invention is made to solve the above-described problems. In other words, an object of the present invention is to provide a gas processing apparatus and a gas processing method that allow gas to be uniformly supplied to the entire surface of a workpiece. Another object of the present invention is to provide a baffle member for use with the gas processing apparatus and the gas processing method.
A first aspect of the present invention is a gas processing apparatus, comprising a processing chamber that is airtightly structured, a gas delivery pipe connected to the processing chamber, a gas supply source for supplying gas to the processing chamber through the gas delivery pipe, a holding table for holding a workpiece loaded to the processing chamber, a shower member disposed at a gas outlet of the gas delivery pipe connected to the processing chamber, a spray plate structured as a partition wall of the shower member that faces the holding plate, the spray plate having a plurality of spray holes, and a baffle member disposed between the spray plate in the shower member and the gas outlet and having a plurality of through-holes formed perpendicular to the surface of the baffle member, wherein each of the through-holes of the baffle member has a first opening portion and a second opening portion facing the gas outlet, the second opening portion facing the spray plate, the opening area of the second opening portion being larger than the opening portion of the first opening portion.
In the gas processing apparatus, the through-holes are formed so that their axes are perpendicular to the front surface of the baffle member.
For example, each of the through-holes is a two-diameter hole. A large diameter hole portion and a small diameter hole portion of each through-hole are connected on one straight line so that the center of the bottom of the large diameter hole portion matches the center of the bottom of the small diameter hole portion (hereinafter, the straight line is referred to as xe2x80x9csame axisxe2x80x9d). When each through-hole has a convex section, the same axis is perpendicular to the front surface of the baffle member.
When each through-hole has two opening portions that are a small opening portion and a small opening portion and the inner wall of each through-hole is tapered as a side surface of a circular cone that connects the two opening portions, the axis of the circular cone is perpendicular to the front surface of the baffle member.
The shape of each through-hole is not limited as long as the center of the first opening portion and the center of the second opening portion are on the normal of the front surface of the baffle member and the opening area of the second opening portion is larger than the opening area of the first opening portion. For example, the shape of each through-hole may be a circle, an ellipse, or a polygon. From view points of easy fabrication and similarity in the parallel direction with the surface of the baffle plate, the shapes of the first opening portion and the second opening portion are preferably circles.
The inner wall surface of each through-hole that connects the first opening portion and the second opening portion may be formed in the above-described convex shape as a two-diameter hole or tapered. Alternatively, the inner wall surface may be formed in a semi-sphere shape. However, from view points of easy machinability and reduction of flow rate of gas flow, it is preferred to taper the inner wall surface.
A typical example of the baffle member according to the present invention is a baffle plate.
The shower member according to the present invention is a shower head. Alternatively, the shower member may be structured by separating a chamber into a plurality of chambers with partition plates and forming a plurality of small holes in the partition plates.
According to the gas processing apparatus of the present invention, since the opening area of the first opening portion of each of the through-holes is smaller than the opening area of the second opening portion of each of the through-holes, when gas delivered from the gas delivery pipe to the shower member flows in the first opening portions of the through-holes, since the flow resistance is large, the backing pressure of the baffle member becomes large.
When the backing pressure of the baffle member becomes large, the irregularity of the dynamic pressure of the gas due to the spray flow from the gas outlet of the gas delivery pipe decreases. Thus, the irregularity of the backing pressure of the baffle member decreases. Consequently, the flow amount of the gas that flows in the through-holes becomes equal.
When the irregularity of the dynamic pressure of the gas that flows in the first opening portion decreases due to a large pressure loss of the gas that flows in the first opening portion, the gas sprays from the first opening portion to the second opening portion that spreads from the first opening portion. The gas that flows in the second opening portion collides with the inner surface thereof and thereby decelerates. In addition, the second opening portion causes the flow rate of the gas to be uniform. Thus, the flow rate of the gas that flows from the second opening portion decelerates. In particular, when the spread angle of the second opening portion against the first opening portion is in the range from 0.5 to 45 degrees, preferably in the range from 1 to 30 degrees, the flow rate of the gas that flows from the second opening portion effectively and largely decelerates in comparison with the flow rate of the first opening portion.
When the opening area of the second opening portion is two times the opening area of the first opening portion, preferably four times that thereof, the average flow rate of the gas decelerates two times larger than that of which the second opening portion, preferably four times larger than that thereof. Generally, the dynamic pressure is proportional to the square of the flow rate. Thus, the dynamic pressure of the gas that flows from the second opening portion is four times smaller than that of which the second opening portion spreads from the first opening portion, preferably 16 times smaller than that thereof. Thus, the uniformity of the backing pressure of the spray plate improves. Consequently, the gas is uniformly supplied to the entire surface of the workpiece (wafer).
A second aspect of the present invention is a gas processing apparatus, comprising a processing chamber that is airtightly structured, a gas delivery pipe connected to the processing chamber, a gas supply source for supplying gas to the processing chamber through the gas delivery pipe, a holding table for holding a workpiece loaded to the processing chamber, a shower member disposed at a gas outlet of the gas delivery pipe connected to the processing chamber, and a baffle member disposed between the spray plate in the shower member and the gas outlet, wherein the gas outlet of the gas delivery pipe spreads toward the shower member.
According to the second aspect of the present invention, the gas outlet is an edge portion of the gas delivery portion disposed in the processing chamber. The gas is supplied from the gas supply source to the processing chamber through the gas outlet.
According to the gas processing apparatus of the second aspect of the present invention, the gas delivered to the gas outlet of the gas delivery pipe collides with the inner surface that spreads and thereby decelerates. In addition, the inner surface that spreads causes the flow rate of the gas that flows from the gas outlet to be uniform. Thus, the flow rate of the gas that flows from the gas outlet decelerates. When the gas outlet of the gas delivery pipe spreads with a spread angle in the range from 0.5 to 45 degrees, preferably in the range from 1 to 30 degrees, the flow rate of the gas that flows from the gas outlet largely decelerates.
In addition, when the opening area of the gas outlet of the gas delivery pipe is two times or more larger than the opening area of the gas inlet of the gas delivery pipe, preferably four times or more larger than that thereof, the flow rate of the gas that flows from the gas outlet much largely decelerates. Thus, the dynamic pressure of the gas that sprays from the gas outlet becomes small and thereby the backing pressure of the spray plate becomes equal. Thus, the gas is uniformly supplied to the entire surface of the workpiece (wafer).
A third aspect of the present invention is a gas processing apparatus, comprising a processing chamber that is airtightly structured, a gas delivery pipe connected to the processing chamber, a gas supply source for supplying gas to the processing chamber through the gas delivery pipe, a holding table for holding a workpiece loaded to the processing chamber, a shower member disposed at a gas outlet of the gas delivery pipe connected to the processing chamber, and a spray plate structured as a partition wall of the shower member that faces the holding plate, the spray plate having a plurality of spray holes, wherein the opening area of the gas outlet of the gas delivery pipe is two times (or more) larger than the opening area of a non-spread portion of the gas delivery pipe.
According to the third aspect of the present invention, the xe2x80x9cnon-spread portion of the gas delivery pipexe2x80x9d is a non-tapered portion of the gas delivery pipe. Examples of the xe2x80x9cnon-spread portion of the gas delivery pipexe2x80x9d are an edge portion that extrudes from the processing chamber and an inlet portion of which the gas is supplied from the gas supply source to the gas delivery pipe.
According to the gas processing apparatus of the third aspect of the present invention, the gas that flows in the gas delivery pipe is delivered to a space (a shower pre-chamber or a buffer chamber) of the shower member through the gas outlet that spreads two times larger than the gas delivery pipe, the flow rate of the gas of the gas outlet is 0.5 times smaller than the flow rate of which the gas outlet of the gas delivery pipe does not spread. Thus, the dynamic pressure of the gas that sprays from the gas outlet of the gas delivery pipe decreases. Consequently, the gas is uniformly supplied to the entire surface of the workpiece (wafer).
A fourth aspect of the present invention is a gas processing method, using a gas processing apparatus having a processing chamber that is airtightly structured, a gas delivery pipe connected to the processing chamber, a gas supply source for supplying gas to the processing chamber through the gas delivery pipe, a holding table for holding a workpiece loaded to the processing chamber, a shower member disposed at a gas outlet of the gas delivery pipe connected to the processing chamber, a spray plate structured as a partition wall of the shower member that faces the holding plate, the spray plate having a plurality of spray holes, and a baffle member disposed between the spray plate in the shower member and the gas outlet and having a plurality of through-holes formed perpendicular to the surface of the baffle member, wherein each of the through-holes of the baffle member has a first opening portion and a second opening portion facing the gas outlet, the second opening portion facing the spray plate, the opening area of the second opening portion being larger than the opening portion of the first opening portion, the gas processing method comprising the step of spraying the gas to the workpiece from the gas supply source through the delivery pipe, the through-holes, and the spray holes, wherein the gas delivered to the first opening portion of each of the through-holes is sprayed to the second opening portion so that the through-holes decelerate the flow rate of the gas.
A fifth aspect of the present invention is a gas processing method, using a gas processing apparatus having a processing chamber that is airtightly structured, a gas delivery pipe connected to the processing chamber, a gas supply source for supplying gas to the processing chamber through the gas delivery pipe, a holding table for holding a workpiece loaded to the processing chamber, a shower member disposed at a gas outlet of the gas delivery pipe connected to the processing chamber, a spray plate structured as a partition wall of the shower member that faces the holding plate, the spray plate having a plurality of spray holes, and a baffle member disposed between the spray plate in the shower member and the gas outlet and having a plurality of through-holes formed perpendicular to the surface of the baffle member, wherein each of the through-holes of the baffle member has a first opening portion and a second opening portion facing the gas outlet, the second opening portion facing the spray plate, the opening area of the second opening portion being larger than the opening portion of the first opening portion, the gas processing method comprising the step of spraying the gas to the workpiece from the gas supply source through the delivery pipe and the spray holes, wherein the gas supplied from the gas supply source is sprayed to the gas outlet of the gas delivery pipe so as to decelerate the flow rate of the gas.
A sixth aspect of the present invention is a baffle member having a plurality of through-holes for partitioning a space of which gas flows in one direction into a first chamber on the upstream side in the gas flow direction and a second chamber on the downstream side in the gas flow direction and for causing the gas to flow between the first chamber and the second chamber, wherein each of the through-holes of the baffle member has a first opening portion and a second opening portion, the first opening portion facing the first chamber, the second opening portion facing the second chamber, the opening area of the second opening portion being larger than the opening portion of the first opening portion, the first opening portion and the second opening portion being connected, the through-holes having an axis perpendicular to the surface of the baffle member.
According to the gas processing apparatus of the present invention, since the opening area of the first opening portion of each of the through-holes is smaller than the opening area of the second opening portion of each of the through-holes, when gas delivered from the gas delivery pipe to the shower member flows in the first opening portions of the through-holes, since the flow resistance is large, the backing pressure of the baffle member becomes large. When the backing pressure of the baffle member becomes large, the irregularity of the dynamic pressure of the gas due to the spray flow from the gas outlet of the gas delivery pipe decreases. Thus, the irregularity of the backing pressure of the baffle member decreases. Consequently, the flow amount of the gas that flows in the through-holes becomes equal. When the irregularity of the dynamic pressure of the gas that flows in the first opening portion decreases due to a large pressure loss of the gas that flows in the first opening portion, the gas sprays from the first opening portion to the second opening portion that spreads from the first opening portion. The gas that flows in the second opening portion collides with the inner surface thereof and thereby decelerates. In addition, the second opening portion causes the flow rate of the gas to be uniform. Thus, the flow rate of the gas that flows from the second opening portion decelerates.
The shape of each through-hole of the baffle member is the same as that of the gas processing apparatus according to the first aspect of the present invention. Alternatively, each through-hole may be formed as a two-diameter hole or tapered. The shapes of the first opening portion and the second opening portion may be circles, ellipses, polygons, or the like.
According to the present invention, whether or not gas has been uniformly supplied to the entire surface of the workpiece is evaluated using a concept of uniformity of gas flow. The uniformity of gas flow can be expressed with the following approximate expression.
Uniformity=(Gmaxxe2x88x92Gmin)/(Gmax+Gmin)
where Gmax is the maximum value of the max flow amount of the gas of the spray holes; and Gmin is the minimum value of the mass flow amount of the spray holes. The reason why the uniformity of the gas flow is represented with such an approximate expression is in that it is difficult to obtain the flow amount of the gas that flows in each spray hole and therefore the mass flow amount of the gas cannot be accurately obtained.
Next, a process for obtaining the uniformity of the gas flow will be described.
Generally, the flow pressure loss dP is given by the following Hagenxe2x80x94Poiseuille""s expression deduced from Fanning""s general expression.
xe2x88x92(dP/dL)=32Uxcexc/D2
where D is the inner diameter of a cylindrical pipe; dL is the infinitesimal distance in the flow direction thereof; U is the average flow rate; xcfx81 is the density of a fluid; xcexc is the viscosity thereof.
Under the operational pressure used in a gas processing apparatus (for example, a CVD apparatus), it can be assumed that gas be applied for equation of state of ideal gas. The difference pressure xcex94P of the gas in the holes can be given by the following expression.
xcex94P={P02+64xcexc LRTG/(MD2)}0.5xe2x88x92P0
where P0 is the downstream pressure of the holes; L is the length of the holes; R is the gas constant; T is the temperature; G is the average mass flow amount of the gas in the holes; and M is the molecular weight of the gas.
When the process pressure in the gas processing apparatus is a relatively reduced pressure, it is considered that the linear velocity of the gas delivered from the gas delivery pipe nearly increases to the sound velocity. Thus, it is necessary to consider the influence of the dynamic pressure of the gas flow. The dynamic pressure PD can be given by the following expression.
PD=(0.5)xcfx81U2
When the maximum difference pressure xcex94Pmax and the minimum difference pressure xcex94Pmin are obtained in consideration with the dynamic pressure PD, the maximum mass flow amount Gmax and the minimum mass flow amount Gmin can be obtained. Thus, the uniformity of the gas flow can be obtained.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.